Communication systems are known to include a communication resource controller, a plurality of communication units, and communication resources. In such communication systems, the communication units communicate with each other via a communication resource, where a communication resource may be an RF channel, a pair of RF channels, a TDM slot, or any medium for carrying RF signals. To initiate a communication, a communication unit transmits a communication request to the communication resource controller via a communication resource dedicated for control information (control channel). The communication request includes a request for a particular service, such as allocation of a communication resource and includes the identity of a target communication unit, or units. For example, the request may be for a group call which identifies all the communication units in the same group as the initiating communication unit.
Upon receiving this request, the communication resource controller determines whether the initiating communication unit is authorized to access the system and, if so, grants the request. Having granted the request, the communication resource controller allocates a communication resource to the initiating communication unit and the target communication units, and then transmits a communication resource allocation message on the control channel. All communication units within the coverage area of the control channel antenna receives the allocation message. However, only the communication units identified in the message, i.e., the initiating and target communication units, will access the allocated communication resource and subsequently partake in the communication.
This method of communication resource allocation works very well in many trunking communication system applications however, because of specific system operator needs, this method has its limitations. To illustrate, assume that a user of a communication device is within a hospital. Further assume that the system operator wishes to prohibit certain types of RF transmissions within the hospital. In these situations, the requesting communication unit is unable to convey a particular RF message to the target communication unit located in the hospital, however, another type of RF message may be available. For example, assume that voice transmissions are prohibited within the hospital, but data transmissions are allowed. If the initiating communication unit requested a voice call, that request would be denied, even though a data message could be executed.
Therefore, a need exists for a method that allows alternate communication services based on geographic location of target communication units.